Centrifugal separators use inertial forces resulting from the acceleration of a material, particularly the acceleration of a material in a circular path, for the separation of a heavier (more dense) material from a lighter (less dense) material. For example, such devices have been found to provide a relatively rapid method of separating immiscible liquids from one another based on different weight phases.
A centrifugal contactor is a type of centrifugal separator that is widely used for liquid-liquid separation, and particularly for solvent extraction processes. These centrifugal separators are termed “contactors” as fluid streams introduced separately into the device are brought together, or contacted, prior to a centrifugal separation of weight phases. For example, fresh water and an organic solvent contaminated with salts may be fed into separate inlets and rapidly mixed in an annular space between a spinning rotor and a stationary housing. The salts may migrate from the organic solvent to the water as they are mixed in the annular space. The water and organic solvent are then centrifugally separated and exit through separate outlets, thus washing salts from the organic solvent with the water.
During normal use, particularly when separating water/petroleum mixtures, solids suspended within the mixture tend to accumulate in the interior of the centrifugal contactor assembly. Such solids are difficult to remove from a welded, enclosed assembly, and back-flushing of the centrifugal contactor has not produced satisfactory results. Better results have been obtained by disassembling the centrifugal contactor and removing the rotor assembly. However, this is a time-consuming operation, and causes the centrifugal contactor to be removed from service for an extended period of time.
To solve this problem, inventors of the present invention disclosed in U.S. Pat. No. 5,908,376 a self-cleaning or “clean-in-place” rotor assembly that can thoroughly clean a centrifugal contactor of accumulated solids without disassembly thereof. The clean-in-place rotor assembly of the centrifugal contactor has a double-ended hollow axial shaft with a bottom end extending through the centrifugal contactor housing. In order to provide a pressurized cleaning solution to the hollow axial shaft, the bottom end of the axial shaft is coupled to a rotary union. The pressurized cleaning solution is then directed from the rotary union into the hollow axial shaft and through a plurality of spray nozzles that are fitted to the axial shaft, which impinges a stream of the pressurized cleaning solution onto the interior surfaces of the centrifugal contactor to remove accumulated solids therefrom.
However, the rotary union used to couple the cleaning fluid supply to the bottom end of the axial shaft has experienced several problems in use. The rotary union is composed of several moving parts, including a bearing and seal assembly that may wear or become damaged during normal use, or during repair or servicing of the centrifugal contactor. Because the rotary union is attached to the bottom end of the axial shaft, the rotary union is otherwise unsupported and, thus, subject to damage due to the constant stress of vibrations from fluid connections and bumps during maintenance or service. The rotary union is also subject to process fluid-related corrosion and wear, resulting in eventual leakage and failure, thus making the rotary union a weak link in centrifugal contactor reliability. This is such a widespread problem with rotary unions that rotary union manufacturers typically limit their warranty to steam, oils, water and other benign fluids. The presence of corrosives, caustics and solids in the centrifugal contactor process streams thus typically voids manufacturer's warranties, as the rotary union is continuously exposed to the process chemistry during the rotary union's installed use in such applications. Additionally, the installation and removal of a rotary union from a centrifugal contactor may require the manipulation of a tool, such as a wrench, in a space between the body of the rotary union and the bottom of the centrifugal contactor, which may be difficult and time consuming.
In view of the above, it would be advantageous to provide improved centrifugal separators and related devices, systems and methods.